Direct Wafer Bonding and Its Application to Waveguide Optical Isolators

Mizumoto, Tetsuya; Shoji, Yuya; Takei, Ryohei

doi:10.3390/ma5050985

Cited by 40 publications

(25 citation statements)

References 62 publications

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“…A surface activated direct bonding technique is a powerful tool to realize a tight contact between dissimilar crystals [24–26]. We developed a surface activated direct bonding technique for integrating a magneto-optical garnet on a silicon waveguide [14]. The surfaces of the target wafers are activated in a vacuum chamber.…”

Section: Magneto-optical Materialsmentioning

confidence: 99%

“…However, it is very difficult to grow garnet crystals on the commonly used optical waveguide platforms such as silicon. We had previously developed a surface activated direct bonding technique to integrate a magneto-optical garnet on silicon and III–V compound semiconductors [13, 14]. Using this technique, a silicon waveguide optical isolator was fabricated for the first time with an optical isolation of 21 dB at a wavelength of 1559 nm [15].…”

Section: Introductionmentioning

confidence: 99%

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Magneto-optical non-reciprocal devices in silicon photonics

Shoji

Mizumoto

2014

Science and Technology of Advanced Materials

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179

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Silicon waveguide optical non-reciprocal devices based on the magneto-optical effect are reviewed. The non-reciprocal phase shift caused by the first-order magneto-optical effect is effective in realizing optical non-reciprocal devices in silicon waveguide platforms. In a silicon-on-insulator waveguide, the low refractive index of the buried oxide layer enhances the magneto-optical phase shift, which reduces the device footprints. A surface activated direct bonding technique was developed to integrate a magneto-optical garnet crystal on the silicon waveguides. A silicon waveguide optical isolator based on the magneto-optical phase shift was demonstrated with an optical isolation of 30 dB and insertion loss of 13 dB at a wavelength of 1548 nm. Furthermore, a four port optical circulator was demonstrated with maximum isolations of 15.3 and 9.3 dB in cross and bar ports, respectively, at a wavelength of 1531 nm.

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Section: Magneto-optical Materialsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magneto-optical non-reciprocal devices in silicon photonics

Shoji

Mizumoto

2014

Science and Technology of Advanced Materials

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179

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“…Discrete isolators rely on Faraday rotation, i.e., a nonreciprocal mode conversion, but in PICs the use of nonreciprocal phase shift (NRPS) in a resonator or interferometer device is preferable to avoid problems caused by the birefringence of optical waveguides. The active material in these isolator devices is commonly a MO iron garnet material, in particular yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) with substituents such as Ce or Bi to increase the MO performance …”

Section: Introductionmentioning

confidence: 99%

Magneto‐Optical Bi:YIG Films with High Figure of Merit for Nonreciprocal Photonics

Fakhrul

Tazlaru

Beran

et al. 2019

Advanced Optical Materials

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lator devices is commonly a MO iron garnet material, in particular yttrium iron garnet (YIG, Y 3 Fe 5 O 12 ) with substituents such as Ce or Bi to increase the MO performance. [5][6][7][8][9][10][11][12][13][14][15] However, the integration of garnets on a Si (or other semiconductor) platform is challenging due to the incompatible lattice parameters and the thermal expansion mismatch between garnets and common semiconductor substrates. [6][7][8][9][10][11][12][13][14][15][16] Moreover, crystallization of the garnet phase usually requires a high thermal budget. Garnets formed on semiconductor substrates are polycrystalline and exhibit higher optical absorption than single crystal films. Furthermore, impurity phases such as YFeO 3 , Fe 2 O 3 , and Bi 2 O 3 can form during the crystallization process, [17] which contributes to optical loss. These factors result in inferior optical performance of polycrystalline MO garnet films compared to the bulk garnet material, and a lower figure of merit (FoM), defined as the ratio of the Faraday rotation to the absorption coefficient per length of the material.Considerable work has been done on growth of garnet films on semiconductors to enable demonstrations of isolators and modulators. [6][7][8][9][10][11][12][13][14][15][16] The first monolithically integrated optical isolator [6] used 80 nm thick Ce:YIG which was grown by pulsed laser deposition (PLD) on a pre-annealed 20 nm thick YIG seed layer to induce crystallization of the Ce:YIG. A simplified PLD process was introduced by Sun et al. [11] where the YIG seed layer was placed on top of the MO garnet and both layers were crystallized simultaneously by rapid thermal annealing (RTA). This top-seedlayer process places the MO garnet in direct contact with the underlying Si waveguide, maximizing the coupling of light from the waveguide to the MO cladding, but it has only been applied to Ce:YIG. Recently rare-earth garnets have been developed that crystallize on Si and quartz without a seed layer, including sputter-deposited terbium iron garnet (TIG) and Bi-doped TIG (Bi:TIG). [18,19] Growth of MO materials on the sidewall of the waveguide can enable a wider range of device designs, including isolators for transverse electric (TE) polarization. Integrated semiconductor lasers emit TE-polarized light, and TE mode isolation using NRPS requires placement of the MO material on the sidewall of the waveguide to break left-right symmetry. [18,20,21] However, the NRPS-based integrated optical isolators that have been experimentally demonstrated are made with the MO material on the top or bottom surface of the waveguide, which isolates only the transverse magnetic (TM) polarization. [6][7][8][11][12][13][14] It is therefore essential to establish deposition conditions that yield Thin film magneto-optical (MO) materials are enablers for integrated nonreciprocal photonic devices such as isolators and circulators. Films of polycrystalline bismuth-substituted yttrium iron garnet (Bi:YIG) have been grown on silicon substrates and waveguide d...

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“…A surface activated direct bonding technique is a powerful tool to realize a tight contact between dissimilar crystals [24][25][26]. We developed a surface activated direct bonding technique for integrating a magneto-optical garnet on a silicon waveguide [14]. The surfaces of the target wafers are activated in a vacuum chamber.…”

Section: Surface Activated Direct Bondingmentioning

confidence: 99%